The present invention relates to postage meters and more particularly to a multiprocessor parcel postage metering system having a serial data bus for interprocessor communications.
A number of different devices and systems have been developed to help a user determine the proper postage for mailing parcels. The simplest of these devices is, of course, a scale which provides visual display of the parcel weight. The operator must translate this weight reading to a postage amount by resort to printed rate charts and special fee charts. The user then applies the postage to the parcel either in the form of stamps or in the form of an adhesive-backed tape printed with the user-calculated postage by a conventional postage meter.
This simple arrangement may be suitable for a conscientious user who mails few parcels over a given period of time. However, if the user isn't conscientious, he may misread the scale or misread the rate charts and incorrectly calculate required amount of postage. If the postage which the user calculates is insufficient, the parcel may be returned to its sender, delaying ultimate delivery. If the calculated postage is excessive, the parcel will be delivered but the user will have wasted his money. Moreover, this approach to mailing parcels is time consuming and cannot be effectively used where any significant number of parcels is to be mailed on a regular basis.
To reduce the chances of human error, it would be possible to develop a completely mechanical parcel metering system in which the displacement of a scale platform could be mechanically translated to a particular postage amount for a given class of service. The calculated postage could then be applied manually either as stamps or as a postage meter imprinted tape. The limitations of such a system are clear. The system would have to be kept simple by limiting its use to a particular class of service. The mechanical construction required to handle several classes of mail would be incredibly complex, making such a device difficult to build and difficult to maintain. Moreover, a mechanical structure could not be easily updated to reflect changes in postal rates or regulations.
Many of the above-discussed problems are overcome in a parcel postage metering system disclosed in U.S. Pat. No. 3,692,988, issued Sept. 19, 1972 and assigned to the assignee of the present invention. That system employs both electromechanical and electronic technologies to generate postage-representing signals as a function of a manually-entered class of service, a manually-entered zone and a parcel weight input to the system in the form of signals from a scale mechanism. This data is used to access a postage memory wherein postage representations are stored as a function of the input data.
The system described above is a highly effective and useful system. However, developments in solid state technology have made it possible to consider a system in which the major components of the system are controlled by individual processors. For example, the scale mechanism would be controlled by its own processor as would the device for setting the meters. Such a multiprocessor system would be considerably more versatile than known parcel postage metering systems. This system could be programmed to handle different classes of service, different special fees and changes in the postal regulations.
One problem which is created in a multiprocessor system is how to transfer data between the different processors of the system. Conventionally, multiprocessor systems have employed parallel data buses with elaborate error checking schemes to assure the integrity of the data. While the conventional data transfer arrangements may be suitable for high speed, large scale multiprocessor systems, the cost and complexity of such arrangements have rendered them impractical for use in systems such as a multiprocessor parcel postage metering system.